Field
The present invention relates generally to systems and apparatus for irradiating targets with electromagnetic radiation, and more specifically to systems having annular-type or various sectored applicators and associated control systems for controlling application of radiation to targets through phased array power steering.
State of the Art
Current systems for applying electromagnetic radiation (EMR) to targets, such as living bodies and biological tissue, and controlling the position of a region of heating within the target through phased array power steering are provided with a plurality of electromagnetic applicators powered by multi-channel EMR systems where different applicators are each provided with electronically controlled power and electronically controlled phase for different channels of the EMR system. This creates a desired phased array heat pattern steering capability.
Several types of therapeutic treatments for cancer in humans are in current, common use. These treatments include surgery, X-rays, radiation from particle accelerators and radioactive sources, and chemotherapy. These treatments are often combined in various ways to enhance treatment effectiveness.
Although such conventional treatment techniques have been successful in treating cancer in many patients and in prolonging the lives of many other patients, they are frequently ineffective against many types of cancer and often have severe adverse side effects at the necessary treatment levels. Protracted treatment of cancer patients by X-rays or chemotherapy, as an example, tends to eventually destroy or inhibit the patients' natural immunological systems to an extent that many patients eventually succumb to common infectious diseases, such as influenza or pneumonia, which otherwise probably would not be fatal. Also, many patients having advanced stages of cancer or complications may become too weak to withstand the trauma of surgical or other cancer treatments so that therapy must be discontinued.
Due both to the prevalence and the typically severe consequences of human cancer, as well as frequent ineffectiveness of current treatments such as those mentioned above, medical researchers are continually experimenting in an attempt to discover and develop improved or alternative cancer treatment methods with their associated treatment apparatus.
Hyperthermia, the generation of artificially elevated body temperatures, has recently been given serious scientific consideration as an alternative means for cancer treatment. Much research has been conducted into the effectiveness of hyperthermia alone or in combination with other treatment methods. This research is important in that hyperthermia techniques appear to have the potential for being extremely effective in the treatment of many or most types of human cancer, without the adverse side effects which are associated with current methods for cancer treatment. Hyperthermia is sometimes called thermal therapy, indicating raising the temperature of a region of the body.
Researchers into hyperthermia treatment of cancer have commonly reported that many types of malignant growths in humans can be thermally destroyed, usually with no serious adverse side effects, by heating the malignancies to temperatures slightly below that which would be injurious to most normal, healthy cells. Furthermore, many types of malignant cell masses have reportedly been found to have substantially lower heat transfer to lessen their ability to dissipate heat, presumably due to poorer vascularity and reduced blood flow characteristics. Consequently, these types of growths appear to be more affected by the hyperthermia treatment, i.e., reach higher temperatures than tissue having normal blood flow. This is referred to as a “therapeutic gain”. Poorly vascularized malignant growths can reportedly be heated to temperatures several degrees higher than the temperature reached by the immediately surrounding healthy tissue. This promises to enable hyperthermic treatment of those types of malignant growths which are more thermally sensitive than normal tissue without destruction of normal cells, and additionally to enable higher temperature, shorter hyperthermia treatment times of more thermally sensitive types of malignancies which exhibit poor vascularity.
In this regard, researchers have commonly reported that as a consequence of these thermal characteristics of most malignant growths and the thermal sensitivity of normal body cells, hyperthermia temperatures for the treatment of human cancer should be carefully limited within a relatively narrow effective and safe temperature range. Hyperthermia is generally provided by temperatures over 40 degrees C. (104 degrees F.). At treatment temperatures above approximately 45 degrees C. (113 degrees F.), thermal damage to most types of normal cells is routinely observed if the time duration exceeds 30 to 60 minutes. Thus, great care must be taken not to exceed these temperatures in healthy tissue for a prolonged period of time. The duration of exposure at any elevated temperature is, of course, an important factor in establishing the extent of thermal damage to the healthy tissue. However, if large or critical regions of the human body are heated above 45 degrees C. for even relatively short times, injury to normal tissue is likely to result. The intent of hyperthermia is to get as much of the tumor region above 40 degree C. as is possible, while not heating the normal tissue above 44 degrees C. If a more selective high temperature can be obtained in the tumor or target tissue, there will be a greater desirable amount of damage done to the tumor or target tissue.
In treating cancerous tissue, it is important to heat all of the cancerous tissue to therapeutic temperatures which can include temperatures well over 45 degrees C., with temperatures over 60 degrees C. desirable in some situations, without heating the normal tissue to temperatures which will injure the normal tissue. Greater tumor or target tissue damage can be obtained at higher temperatures. The goal of most hyperthermia systems is to be able to heat the tissue in need of treatment without heating the normal tissue surrounding the tissue in need of treatment. Therefore, to provide such treatment it is desirable to have a hyperthermia system which can provide a heating zone about the size of the tumor or other diseased tissue to be treated and it is critical to provide this heating zone at the location of the tumor or other diseased tissue to be treated. This can be particularly difficult in treating tumors or other tissue to be treated that is located deep within a relatively large mass of normal tissue, such as within a human torso, i.e., within the pelvis, abdomen, or thorax. The torso of an adult human is typically of a size having diameters between about 22 cm and 33 cm. A tumor or other tissue deposit to be treated in a human pelvis, abdomen, or thorax typically has a maximum diameter of about 8 cm or less and may be located in various positions within the pelvis, abdomen, or thorax. Most of these are located deep within the normal body tissue, as opposed to near the surface of the normal tissue (skin), and require what is referred to as “deep-heating”.
Hyperthermia systems using phased arrays of radio frequency radiating applicators arranged noninvasively around an area of the body containing a tumor or other tissue to be treated, such as the pelvis, abdomen, or thorax, are commercially available. Extensive articles and reports have been written on the use of these phased array systems to provide hyperthermia heat pattern steering, and several patents have been issued covering the use of phased arrays, see, for example, U.S. Pat. Nos. 5,097,844 and 4,672,980. All of these systems rely upon the use of electronic phase and power steering to provide heat pattern focusing and steering control. When radio frequency signals are directed into a body portion from several applicators arranged around the body portion, these signals are superimposed within the body portion to provide areas of constructive interference and areas of destructive interference. The areas of constructive interference are areas of heating with maximum heating occurring where the largest number of superimposed signals constructively interfere. In a phased array hyperthermia system, the phase and amplitude of each signal is chosen so that theoretically all of the signals directed into the body will be superimposed to constructively interfere and provide maximum heating at the location of the tissue to be treated and will form a heated focal zone at that location. This heated focal zone should be of a temperature and size to heat the entire area of tissue to be treated to the desired minimum temperature for treatment while not heating surrounding tissue to an extent to cause damage to this surrounding tissue. As indicated above, it is important to limit the heating of the normal tissue surrounding the tissue to be treated. However, although not preferred, in many instances some destructive heating of normal tissue surrounding the tissue to be treated can be tolerated to ensure that all tissue to be treated is heated to the critical temperature. It is also important that hot spots that could damage normal tissue are not created in areas of normal tissue away from the tissue to be treated or away from the tissue immediately surrounding the tissue to be treated.
The BSD-2000 system produced by BSD Medical Corporation, Salt Lake City, Utah, is a radio frequency annular phased array hyperthermia system for heating deep seated tissue to be treated in a relatively large diameter tissue mass such as a human torso. The system provides three rings of multiple radio frequency applicators, such as radio frequency dipole antennas or radio frequency dipole antenna pairs, with the applicators of each ring spaced around an opening adapted to receive therein the body portion having the tissue to be treated. The respective rings are spaced or stacked along the longitudinal axis of the body portion having the tissue to be treated. Separate power channels control the frequency, radiated power, and relative phase of the radio frequency energy radiated by each applicator or combination of selected applicators. Such a system is described in U.S. Pat. No. 5,097,844. Each channel is connected to an antenna or an antenna pair in the array and has separate electronic controls for the power and phase of the radio frequency signal sent to the connected antenna, antenna pair, or combination of selected antennas or antenna pairs. This allows electronic steering and focusing of the heating pattern. The most advanced phased array applicator configuration currently used with this system is called the “Sigma Eye”, and contains three rings of dipole antennas as described in U.S. Pat. No. 5,097,844. However, rather than circular rings as shown in U.S. Pat. No. 5,097,844, the rings of the Sigma Eye applicator are elliptical in shape. The Sigma Eye elliptical rings provide improved comfort for patients over circular rings and maximizes the 3D energy convergence at the targeted treatment location. The use of three rings of applicators allows three dimensional steering and focusing of the heating zone created by the antenna array. U.S. Pat. No. 4,672,980 teaches a system having an antenna array containing two rings of dipole antennas to provide two dimensional steering and focusing of the heating zone created by that antenna array. It should be noted that in the present application, as shown by the Sigma Eye configuration disclosed, “ring” is not used to mean circular, but to mean a plurality of applicators spaced around an opening adapted to receive a body part so that with a body part received in the opening the applicators of the ring are spaced around the body part in a manner to direct the radio frequency signals into the body part. The rings can take various configurations, which can be, for example, a circular configuration, an elliptical configuration, a rectangular configuration, a triangular configuration, or other configuration surrounding the tissue to be heated. Similarly, while such systems are generally referred to as annular phased array systems, the use of the term “annular” does not limit the system to circular arrays but to arrays having any shape as indicated above for the meaning of ring.
Prior art phased array systems have successfully used radio frequency signals up to 120 MHz to provide deep heating of tissue in the human torso which includes the pelvis, abdomen, and thorax. The commercial BSD-2000 system using the Sigma Eye as described above has been limited to use of radio frequency signals no greater than 100 MHz when used for deep heating. This frequency limit was chosen in order to provide sufficient penetration of the radiation deep into the tissue to provide a controlled heated focal zone deep in the tissue without producing hot spots in other parts of the tissue away from the heating zone. In order to obtain optimum localization of heating at depth it is necessary to use a frequency low enough to have sufficient penetration and limit the formation of standing waves that could produce hot spots in the tissues away from the desired heated focal zone. There is no data indicating that a frequency above 100 MHz can provide an adequate deep central heated focal zone in the relatively large tissue mass of the adult torso. Also, it was expected that the use of higher frequencies would have the potential for creating multiple hot spots within the normal tissue away from the desired heated focal zone due to the standing waves. The current BSD-2000 system uses a maximum operating frequency of 100 MHz for deep body heating and uses 12 RF power and phase control channels to drive 12 pairs of linear dipole antennas as described in U.S. Pat. No. 5,097,844. This system provides deep heating of the pelvic, abdominal, and thorax regions of an adult with a heated focal zone volume of 1,500 to 5,000 cubic centimeters at a frequency of 100 MHz. The 1,500 cc volume corresponds to a primary heating volume with a diameter of 14 cm in each of the three orthogonal axes. However, as indicated above, most target tumors deep in the body are much smaller than this size, typically with a diameter of less than 8 cm. Using frequencies at or below 120 MHz in a noninvasive antenna array system forms a spherical focus for the heated focal zone which has a major axis diameter of 20 cm or greater. When the focus is spheroidal, using frequencies no greater than 120 MHz, it is possible to lessen one dimension to as small as 10 cm, but then the other maximum diameter dimension is greater than 20 cm. This is much larger than the typical size of the tissue needing heat treatment so substantial volumes of normal tissue around the deposit to be treated will also be heated and damaged. The use of higher frequency RF signals can theoretically reduce the size of the heating zone produced by the interacting signals. Some reports have indicated that frequencies as high as 434 MHz have been used with annular type phased array systems for producing smaller heating zones in body parts such as limbs or the neck region of a body. Such high frequencies can be used in these regions due to the much smaller total tissue mass size for these regions of the human body. With these smaller sized body parts, deep tissue penetration is not needed.
While the U.S. Pat. No. 5,097,844 discloses that the theoretical focal zone size can be reduced by using higher frequencies, it does not disclose how such a system could be implemented to provide a small and deep focal zone size and a selectively heated focal zone at depth in the tissue. Further, the patent does not disclose how the deep local heated focal zone could be preserved when phase and amplitude steering is done to direct the smaller heated focal zone to a targeted treatment site. Therefore, there is a need to develop a means to utilize higher operating frequencies to reduce the size of the heated focal zone. To accomplish this requires special design considerations and limitations that were not foreseen or included in U.S. Pat. No. 5,097,844. The higher frequencies have not been used in prior art systems for deep tissue heating. The inventors have found that the use of higher frequencies to enable smaller heated focal zones in deep tissue heating require special design constraints for the annular phased arrays and changes in the bolus interface media between the applicator array and the human body. The dependence of body size, the size of the targeted tissue, the array size, the array shape, the number of radiating applicators, the number of independent RF power and phase control channels, the bolus interface media, and the operating frequency must all be considered in the design in order to achieve a desired selective deep heated focal zone.
There is a need for EMR applicator apparatus, and corresponding methods for EMR irradiation, which provide a more localized deep focal heating of deep tumors or otherwise diseased tissues in the body and to provide more selective target tissue heating with reduced heating of other normal tissues. The need is that the heating zone should penetrate to the center of the torso of an adult body and be capable of selective heating in a targeted region that is approximately 8 cm in diameter or less. Thus, at all points within a sphere with a diameter of 8 cm, corresponding to a volume of 270 cubic centimeters of tissue, the relative SAR (Specific Absorption Rate, or absorbed power per unit mass) would be within 50% of the maximum SAR within the sphere of targeted tissue. It is not necessary that the heating zone be completely confined to the tumor target area, but that there is greater localization than currently available to minimize the excessive heating of normal tissues. If more selective deep heating is provided, it is expected that the target tissue could be heated to a higher temperature than is currently possible, thereby increasing the therapeutic benefit of the hyperthermia treatment without increasing toxicity to the body.